1. Field of the Invention
The invention relates to a method for forming composite materials, more particularly to a method for forming polymer-blend nanocomposites using a nanocompatibilizer.
2. Description of the Prior Art
Due to the rising consciousness on the environmental protection, the development of various biodegradable polymers has been received much attention by the industry in recent years, especially the biodegradable polymers applied in the packaging industry. However, the price of biodegradable polymers is usually quite high, and the mechanical properties such as tearing resistance etc. are inferior to the conventional packaging materials, such as polyethylene (PE). Therefore, for a biodegradable polymer to be commercialized successfully, it should be prepared through a blending process. In particular, the starch-based biodegradable polymers are widely studied due to the relatively low price of raw starch materials. However, there is quite a lot of moisture sensitivity problem for these starch-based biodegradable polymers, which in turn may affect their mechanical properties by some parameters. To better understand this behavior, nonpolar metallocene catalyzed polyolefin elastomer (mPE) was selected to blend with starch as an illustrative system for the current invention.
Furthermore, because different polymers show different properties, two kinds of polymers are often blended together to obtain a required property, which is a conventional way to produce the commercialized products. In general, the compatibility of different polymers is usually not good, thus a compatibilizer is often added to improve the compatibility of different polymers. Specifically, a clay-reinforced compatibilizer, termed nanocompatibilizer, was added to improve the interfacial strength of mPE/starch blends by exploiting the concept of nanocomposites.
In 1988, Toyota Company in Japan issued Nylon 6/clay nanocomposite patent (U.S. Pat. No. 4,739,007) at the first time. The organic alkyl ammonium was used to exchange the cations of silicate within the inorganic clay gallery, and to modify the hydrophilic clay into hydrophobic nanoclay. With the addition of modified clay during the in-situ polymerization of Nylon 6, the heat distortion temperature and mechanical properties of pristine Nylon 6 were improved significantly. Especially the above-mentioned efficacy could be reached by adding only a small amount of clay (about 3 to 5%), which was different from the conventional composite with high loading of inorganic substance (about 20%). It became the earliest commercialized nanocomposites.
Moreover, in 1992 Toyota Company cooperated with the Ube company to improve the modification technique of nanoclay. The Nylon 6 monomer, ω-caprolactam, was grafted to Na+ type Montmorillonite nanoclay directly. Then it was polymerized to form the exfoliated type Nylon 6/clay nanocomposite (U.S. Pat. No. 5,102,948). The tensile strength, tensile modulus, flexural modulus and heat distortion temperature etc. were increased significantly. Additionally, the dimensional stability, gas barrier property and flame retardant property etc. were much better than those of conventional Nylon 6 composites.
To exploit the uniqueness of nanoclay, in U.S. Pat. No. 6,339,121, Rafailovich et al. used the modified nanoclay as a compatibilizer for incompatible polymers. The patent pointed out that the organic modified nanoclay could be added into polymer blends, in order to improve the compatibility between two incompatible polymers, and to develop a more homogeneous system as well. However, this kind of system must be annealed at high temperatures for a day to promote the compatibility of incompatible polymers.
Upon searching and reviewing the prior art, the patented invention of relevant technology is still insufficient, and there is little research and development on any relevant technology, so more efforts should be made in the industry in the future.
Upon assessing the technological development of the prior art, although polymer/clay nanocomposites have established a milestone for major technological development in recent years, in fact the performance/cost ratio should be considered carefully in future applications. Therefore, up to date only a few nanocomposite systems are commercialized successfully.